The ability to pinpoint the location of mobile telephones is a desirable feature of a mobile telephone network. This is because of the need to provide customer services which rely on knowing the whereabouts of users of these services. For example, up-to-date local traffic information can be provided to enable a user to avoid nearby traffic jams. A user may also wish to know, for example, how to get to the nearest pub or restaurant from their present location. Clearly the location of the user must be ascertained to within even a few metres for this type of service to work.
Another reason for wishing to know the location of a mobile telephone is so that emergency services can locate a caller who is unable to provide an accurate personal location themselves.
The ability to pinpoint the location of a mobile telephone normally relies on ascertaining its position relative to known positions of mobile network entities such as base stations. It is known in the art and has been observed by the present inventors during mobile station location trials, that it can be very difficult to obtain accurate information about mobile telephone networks. Examples of problematic information include base station coordinates, base station identities and transmission channels used. This type of data is provided by the network operator and it is quite common for such data to be incorrect, for example because it has not been updated.
One specific problem is incorrect base station coordinates. If it is intended to pinpoint the location of a mobile telephone relative to a base station, it is clear that any location of the mobile telephone calculated on the basis of the base station coordinates will also be incorrect. The present inventors have noticed errors of up to several hundreds of meters in different countries in base station positions. Such large errors clearly have a negative impact when providing the type of customer services described above.
Another specific problem arises when base stations are identified wrongly. For example, in a GSM network a base station can be identified by its Broadcast Control Channel (BCCH) frequency and Base Station Identity Code (BSIC) value. This information is also provided by the network operator and if it is not correct, the wrong base station is identified, and its coordinates are used, which in turn means that the wrong coordinates are used for the calculation of mobile telephone location. Clearly, even with a relatively large number of base stations in a given network area, using the wrong coordinates could have a significant impact on the calculated mobile telephone position and hence the ability to advise the user of local information.
Yet another specific problem is that, depending on the particular operator, the transmission channels used might be changed relatively often. If non-updated channel information is used for mobile station location calculation, when frequencies have been changed, again, base stations are incorrectly identified.
It is also useful to know base station co-ordinates for the purposes of network planning to allow normal call and data operation. Even though the accuracy required for this is less than that required for the above-described location services, errors of several hundred meter can also cause problems in network planning.]
It would be desirable to provide a method of checking the consistency of network information such as the operator-provided information described above. Ideally such a method would be easily implementable in networks supporting E-OTD location method in GSM, and OTDOA-IPDL method in UMTS.